Scientific Investigations Report 2014–5147
Sediment fingerprinting quantifies the delivery of fine-grained sediment from a watershed and sediment-budget measurements quantify the erosion and deposition of fine-grained sediment. Both approaches were used in the agricultural and forested 147-square-kilometer (km2) Linganore Creek watershed in Maryland from August 1, 2008 through December 31, 2010, to determine the sources of fine-grained (less than 63 microns) sediment, and the amount of fine-grained sediment eroded from and deposited on streambanks, flood plains, channel beds, and agricultural and forested uplands. Sediment-weighted results of sediment fingerprinting for 194 suspended-sediment samples collected during 36 storms indicate that streambanks contributed 52 percent of the annual fine-grained suspended-sediment load, agriculture (cropland and pasture) contributed 45 percent, and forests contributed 3 percent. Fifty-four percent of the Linganore Creek watershed is agriculture and 27 percent is forest.
Sediment-budget calculations were based on field measurements and photogrammetric analyses and indicated that the highest percentage of fine-grained sediment was eroded from agriculture (86 percent), followed by streambanks (10 percent), forests (3 percent), and the channel bed (less than 1 percent). Results of the sediment budget indicated that the highest percentage of fine-grained sediment was stored in ponds (57 percent), followed by flood plains (32 percent), streambanks (6 percent), and the channel bed (5 percent). Typical of most sediment budgets, the final sediment budget indicated erosion of 4.70 x 107 kilograms per year (kg/yr), which is higher than the fine-grained suspended-sediment load leaving the watershed (5.45 x 106 kg/yr). The differences in the sediment budget and the measured mass leaving the watershed could be due to an overestimation of erosion using the Cesium-137 method and (or) not adequately defining and measuring storage areas.
Management implications of this study indicate that both agriculture and streambanks are important sources of sediment in Linganore Creek where the delivery of agriculture sediment was 4 percent and the delivery of streambank sediment was 44 percent. Fourth order streambanks, on average, had the highest rates of bank erosion. Combining the sediment fingerprinting and sediment budget results indicates that 96 percent of the eroded fine-grained sediment from agriculture went into storage. Flood plains and ponds are effective storage sites of sediment in the Linganore Creek watershed. Flood plains stored 8 percent of all eroded sediment with 4th and 5th order flood plains, on average, storing the most sediment. Small ponds in the Linganore Creek watershed, which drained 16 percent of the total watershed area, stored 15 percent of all eroded sediment. Channel beds were relatively stable with the greatest erosion generally occurring in 4th and 5th order streams.
First posted March 31, 2015
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Gellis, A.C., Noe, G.B., Clune, J.W., Myers, M.K., Hupp, C.R., Schenk, E.R., and Schwarz, G.E., 2015, Sources of fine-grained sediment in the Linganore Creek watershed, Frederick and Carroll Counties, Maryland, 2008–10: U.S. Geological Survey Scientific Investigations Report 2014–5147, 56 p., http://dx.doi.org/10.3133/sir20145147.
ISSN 2328–0328 (online)
Sources of Fine-Grained Sediment
Summary and Conclusions
Appendix 1. Percentage of silt and clay in suspended-sediment samples collected at Linganore Creek, Md. between July 18, 2008 and August 28, 2009.
Appendix 2. Summary of tracers analyzed from fluvial samples collected in Linganore Creek, August 1, 2008 through October 1, 2010.
Appendix 3. Summary of tracer results for streambank source samples.
Appendix 4. Samples taken for sediment-source analysis in agricultural (cropland and pasture) areas.
Appendix 5. Summary of tracer results for forest source samples.
Appendix 6a. Summary of sediment-source results for the 36 sampled events.
Appendix 6b. Minimum and maximum temperatures recorded at the Frederick Airport, Md. for sampled storms that occur in late fall to early spring.
Appendix 7a. Summary of sites where pins were installed to measure streambank changes.
Appendix 7b. Summary of flood-plain measurements made at Linganore Creek, Md., August 1, 2008 through December 31, 2010.
Appendix 8. Proportion II model results on 137Cs measurements made on agricultural sites, Linganore Creek, Md.
Appendix 9. Diffusion and migration model results on 137Cs measurements made on forested sites, Linganore Creek, Md.
Appendix 10. Summary of 137Cs at reference sites in Linganore Creek, Md.
Appendix 11. Characteristics of ponds in the Linganore Creek watershed.
Appendix 12. Measurement uncertainty in bank pin measurements, Difficult Run, Va., July 8, 2011.
Appendix 13. Measurement uncertainty in flood-plain pad measurements, Difficult Run, Va., July 15, 2011.